Computer Network And Telecommunication

Data communication: The process of transferring data or information between computers called data communications.

Telecommunication: It refer all types of data transmission like characters, numerical, photos, audios and videos etc using electronic or light emitting media.

Cables (Guided Media): Cables are the most common transmission media. Two or more devices are connected directly using cables. Three types of cables are used in computer networking they are:

Twisted pair cable: Twisted copper cables are used only for lower bandwidth. It consists of two isolated strands of copper wire twisted around each other. There are two types of twisted pair cables they are as follows:

UTP (Unshielded Twisted Pair): UTP cables does not have metal shield expect plastic coating. It contains number of twisted pairs of wires with a simple plastic casing. It commonly used to for LAN and Telephony. It is cheaper and easier to work with, but do not offer high bandwidth and good protection from interferences. It can support data transmission rates from 10 to 100 mbps.

STP (Shielded Twisted Pair): STP is similar to UTP but it is shielded with metal sheath along with plastic coating. It offers high bandwidth and good protection from interferences. It is cheaper than fiber optic cable. It can support data transmission rates from 10 to 500 mbps.

Co- axial cable: A co-axial carries higher bandwidth than twisted pair, it is easy to connect. It does not bend readily. This cable consists of one or more small cables in a protective covering. It offer very high data transfer rate and can be placed underground and laid on the floors of lakes and oceans.

Fiber Optic cable: Fiber optic cable is a thin filament of glass fiver wrapped in a protective jacket. It consists of strands of glass like thread, each about the diameter of a human hair. It offer high-speed data transmission rate because data travel as high-speed pulses of light.

Summary of Cable Types (Not important for examination point of view)

Cable Type

Susceptibility to Interference

Transmission Speed

Maximum Distance

Installation Difficulty

Thin coax

Low

10 Mbps

185 meters

Low

Thick coax

Very low

10 Mbps

500 meters

Difficult

UTP

High

10 to 100 Mbps

100 meters

Easy

STP

Low

10 to 500 Mbps

90 meters

Moderate

RS-232

N/A

20 Kbps

50 Feet

N/A

Infrared

High

115 Kbps-4 Mbps

1 meter

Easy

Fiber-optic

None

100 Mbps to 1Gbps and beyond

Up to 30 miles

Difficult

Wireless (Unguided Media): It is used to transfer data with in a large geographical areas or globally without the use of interconnecting wires or cables. It uses other components such as radio signals, microwaves, or infrared to connect network.

Types of wireless communication:

Microwave Systems: Microwave signals are similar to radio and television signals and are used to transmit data through the space without the use of cable. It provides high-speed data transmission. These signals cannot bend or pass obstacles like hills and tall buildings, so very high towers are used to mount the signals. The transmission is limited about 30 miles. Chain of towers is required to transmit the microwave signals in a long distance

Satellite communication:Both microwaves signals and telephone signals can be relayed to a earth station for transmission to a communication satellite. The earth station consists of a satellite dish that functions as an antenna a communication equipment to transmit and receive data from satellite passing overhead. It is not disturbed by hills and tall buildings and visible from any point. So sender and receiver easily communicate with each other using antenna by aiming the satellite. It is very expensive for placing satellite along the earth orbit.

Modulation: The process of changing some characteristics (amplitude, frequency or phase) of carrier wave in accordance with the intensity of the signal is known as modulation.

Types of modulation:

Amplitude Modulation (AM)

Frequency Modulation (FM)

Phase Modulation (PM)

Mode of communication:

Simplex mode: Simplex is one-way data transmission that takes place only from sender to receiver. An example of this would be a television that allows the signal to pass in only one direction. Computer network connections do not use simplex.

Duplex mode: Duplex is two-way data transmission that takes place both directions over a communication channel. Computer use duplex channel. For example if computer A and computer B are connected together than both computer can share data or information. From computer A to computer B or computer B to computer A.

Types of Duplex Mode:

Half duplex: Half duplex is two way data transmission that takes place in only one direction at a time

Full duplex: Full duplex is two-way data transmission that takes place in both directions at a time.

Computer Network: A computer network is a logical or physical interconnection between two or more computers such that they could communicate with each other. It is used to provide users with the access to share resources. These shared resources include data files, application software and hardware.

Components of computer network.

Computer

Transmission media

Network software.

Protocols.

Networking cables.(Transmission media)

Advantages and disadvantages of computer network.

Advantages of computer network:

Resources, data, software and hardware can be shared.

Faster & cheaper communication and data transmission.

It provides as the tools for e-mail teleconferencing videoconferencing which facilities communication.

Flexible working condition.

Office automation can be making very effective well managed.

Disadvantages of computer network.

High installation and administrative cost.

Attack on the privacy of the people.

Computer virus spread most easily through network.

Technologically very complicated.

If the server is out of order, then all workstations are hang up.

Well trained technical support is required.

Network architectures or (Types of Network Architecture) or LAN Architecture:

Client server: This is old model of computer network. In this kind of network model one main computer equipped with very powerful processor, large memory and network operating system works as a main computer or service provider. Other computers connected with server, which are also called workstation or node or terminals can use the hardware and software resources of server computer. There are different types of server such as file server, print server, network server or email server.

Advantages of client server network:

It works with any size or physical layout of LAN.

It does not tend to slow down with heavy use.

The network can be expanded to any size as we wish.

It provide very high level security

It reduces software installation time and cost to all computers.

Disadvantages of client server network:

It is very difficult to setup and well trained technicians are required to handle and setup.

It is expensive compare to peer to peer network.

All software and operating systems are installed in server computer so that other client computer has to depend on it.

Peer to peer: It is also called workgroups also. Because all computers in the network have equal responsibilities. All computers in the network have access to at least on e or more computers. It mostly used in LAN and every organizations, research centers such as banks, travel agencies, airlines educational institutions etc.

Advantages of peer to peer network:

It is easy to setup.

Users in each computer can determine the resources to be shared among other computers.

Any required software can be installed on individual computers , they don’t have to depend on the server.

It is suitable at home, office, banks and small organization.

It is cheaper compare to client server network.

Disadvantages of peer to peer network:

It is slow because of heavy load.

It is suitable for limited area such as school offices and small organization.

The network expansion is limited and can not be expanded as the wish.

It has limited security level.

Types of computer network:

Local Area Network: The way of connecting two or more computers in a very limited area (about 100 to 300 meters) or within a same building or a group of adjacent building is called LAN. It enables very high speed communication through wire connection or wireless connection some times. Small organizations prefer it because of less expensive and faster communication.

Metropolitan Area Network: The way of connecting computers inside a metropolitan area is called MAN. The area may be a part of city, whole part of city, district, zone or country. Radio wave is used to transmit the data for communication between the workstation and server in the system. Many different systems of networking and computing are brought together to form a MAN.

Wide Area Network: The connection of computers of networks covering more distance or the world by the help of wave, frequency and satellite is called WAN. Different types of LAN and MAN are connected to form a WAN. It covers more area but it is slower than LAN and MAN.

Network Topology: Set of rules and regulations, which are essential for networking are called topology. It may contain software, hardware or geographical situation of the networking. Or in another words it is the pattern in which the computers are interconnected.

Types of Network Topology:

BUS Topology.

Key Features

Advantages

Disadvantages

Uses a single length of cable to interconnect network devices.

The failure of one computer does not affect the performance of the rest network.

It tends to slow down under the heavy load.

Uses terminators to dampen signal reflection at the ends of the cables.

Computers can be easily added or removed from the network.

Commonly uses coaxial cable, which is prone to cable breaks. This will disrupt network use.

Network devices connect directly to the cable.

Less physical cable is required to make the network. So it is cheaper and easy to implement.

If a cable break or problems occur, the entire network goes down.

Ring Topology:

Key Features

Advantages

Disadvantages

Devices are connected in a ring formation.

1. Each computer does not have to depend on the central computer as each computer controls transmission to and form it self.

1. If a single computer fails, at least a portion of the network will not work.2. It is difficult to change the network structure.

A star ring uses an MSAU (Multi-station Access Unit) to form the ring function internally.

2. Devices in a star ring configuration can be added and removed without network disruption.3. It has short cable connection, which increases the network reliability.

4. It support very high data transmission rate

3. The MSAU in a star ring provides a single point of failure.4. An extensive rewriting must be done to maintain the ring structure when computers are added or removed.

Star Topology:

Key Features

Advantages

Disadvantages

Most commonly implemented network topology used today.

1. Computer systems can be added or removed from the network without disrupting network users.

1. If centralized device (hub/switch) fails whole network goes down.

Uses individual cables to connect each device to the network.

2. A cable failure affects only the network device connected to it.

2. Because each device requires its own length of cable, more cable is required than in a bus topology.

Problem isolation is straight forward.

3. When a device fails in a star topology, it can be easier to trace the location of the problem.4. It support very data transmission rate.

5. It is more reliable

3. Additional network equipment such as the hub or switch is needed to make the network connection. So it is costly.4. It is difficult to expand.

Different devices and terms used in Network:

MODEM: Modem is a device that directly converts digital signal from a computer or other digital devices into analog form for transmission over analog link i.e telephone line and vice versa. MODEM stands for Modulation and Demodulation. There are two types of modem used in computer they are as follows:

Internal modem b. External modem.

NIC: It is a Network Interface Card, which connects each computer to the wiring to the network. A NIC is a circuit board that fits in one of the computer’s expansion slots. It provides a port on the back of the computer to connect in the network.

Hub: Hubs are connectivity devices, which contain multiple ports for connecting to network components. Hubs connect the computers in a star topology. It lies between server and clients computers.

Connector : Bridge and Gateway are the two different connectors, which play role to link between two network systems.

Bridge: Bridge connects networks using same communications protocols or similar networks so that information can be passed from one to the other.

Gateway: Gateway connects networks using different communications protocols or dissimilar networks so that information can be passed from one to the other.

Switch: A device that capable of forwarding packets directly to the ports associated with particular network addresses. Hubs and switches are almost same but switch is new technology and intelligent compare to hub.

Repeater: A device used on communications circuits that decrees distortion by amplifying or regenerating a signals so that it can be transmitted onward in its original strength and form as they pass through a network cable.

Protocols: Protocols are the set of rules and formats for sending and receiving data. It works as guidelines to govern the exchange between equipments. There are different types of protocols that we can use. Some of popular protocols are TCP/IP, HTTP, FTP, IPX/SPX.

Router: A router is a device that is used to connect different LAN in the network. It receives transmitted messages and forwards them their correct destinations over most efficient available route.

Note: Band width : The amount of data that which is sent through a data-transmitting medium, such as a computer network, telephone line, or coaxial cable, in a given amount of time is called band width.

Note: Bits : In computer processing and storage, a bit is the smallest unit of information handled by a computer and is represented physically by an element such as a single pulse sent through a circuit or a small spot on a magnetic disk capable of storing either a 1 or a 0.

Chapter: Multimedia Multimedia : The technology of combining speech, hypertext, text, still graphics, animation, moving pictures and sound using the computing power of PC is known as multimedia. For example TV shows, because it has a feature of interactive. Multimedia Technology: Multimedia technology is a special computerized technique, which helps the user by providing techniques to combine texts, pictures, sound and video films including interactive facilities. It also provides facilities to the user to create store, edit, delete and copy those data in the computer with the help of specific computer program such as Microsoft Power point, Adobe Acrobat, Macromedia Flash etc. Multimedia Hardware: Multimedia system requires some additional set of hardware to support such multimedia presentation are as follows. Computer set Sound card Sound blast DVD-ROM Microphone Headset Digital camera Video adapter etc. Multimedia Application: Multimedia is used for any computer application in which text alone does not work. Multimedia has become a prerequisite for computer games of all kinds. Its use is growing in computer based education (CBE) and computer based tanning (CBT). Now a days computer’s use is increase day by day and almost all sector of the world is computerized and use of multimedia technology is also increase. There any different types of computer application available in the market. The choice is depend on the requirements and the performance of the computer itself. Some of them are categorized as follows: Paint program format such as: Bit Mapped Graphics (BMP or Windows Bitmap. Graphics Interchange Format (GIF). Joint Photographic Expert Group (JPEG). Protable Network Graphics (PNG). Image Editors or Software such as: Adobe Photoshop PhotoDeluxe CorelPhotopaint Drawing programs or software such as: Macromedia Freehand Adobe Illustrator. Core Draw Video Editors Software and format such as: Motion Picture Experts Group (MPEG-2) Quick Time (Format) Video for windows (AVI format) Adobe premiere software Video VisionML Software Video Vision Studio Software Avid Cinema Software Fusion Recorder Software Maya Software Audio software and format such as: MP3 format Sun/Next (AU) sounds. Microsoft Windows Wav sounds format. Musical instrument digital interface (MIDI) format. Sound Forge (Sound Editor) SoundEdit (Sound Editor) Multimedia Deck (Sound Editor) Creating multimedia: The process of multimedia work involves several steps. Some of the important steps are listed below: Planning the work. Creating and collecting the elements to be included in the work. Combining the elements to create the work Testing, evaluating the refining the work Writing the work to a portable storage medium such as a CD-ROM or posting the work on the web. There are three common ways to organize or planning the multimedia work. They are as follows: Sequential page based multimedia: The simple pages which containing slides of text, pictures, still graphics, videos is called sequential page based multimedia. This type of multimedia presentation is used in college and school for lecture and advertisement in sales company and other various purposes. Hypertext based multimedia: This type of multimedia is attached with hypertext document in the web. It provide link to the containing folder or files or pictures and articles. Any type of multimedia can be used such as graphics, sound, video animation. Movie based multimedia: the work can be a movie or series of movies that stop from time to time to enable the user to follow a link. Virtual Reality: Creation of 3D animations and games to control flying and running items is virtual reality. Some time while using such multimedia with Head-Mounted Display (HMD), a helmet like contraption equipped with stereo LCD displays. We feel like exploring in the room or earth in a very complex virtual environment. The most advanced immersive technology to date is the Cave Automotive Virtual Environment (CAVE). In WWW Virtual Reality Modeling Language (VRML) is used to create such virtual reality animation. It is mostly used in computer games to give real experience in virtual environment. Advantages of Multimedia: It helps to create effective presentation and tutorial material for all subjects. It is very portable so that it can be used at any time anywhere by anybody. Very easy to use, handle, carry, copy and store. Very helpful to transfer messages and advertisements in WWW. It provides very powerful presentation tools with colored pictures, motion pictures and other. Disadvantages of Multimedia: Very expensive installation cost. Require a well trained manpower or technician. Expensive hardware components. Inaccessible to poor due to high cost.

IT Policy Of Nepal 2002 A.D (Suchana Prabidhi Niti 2057 B.S)

The information technology (IT) policy, Nepal was adopted in 2002 A.D i.e 2057 to define the visions, background, objectives and strategies of computer education in Nepal. Below, we briefly discuss the important ones:

Vision: “To place Nepal on Global Map of Information Technology within next five years,” is the main vision of IT policy of Nepal 2002.

Objectives /Purposes of the IT policy 2002 of Nepal are as follows:

To create knowledge based society

To create job opportunities for the people.

To establish knowledge based industries.

Main polices of IT policy of Nepal

To flow the information after the development of web site of all ministries and departments of government.

To develop E-commerce

To develop E-education

To develop E-health

Work policies of IT policy of Nepal

To develop the communication system if local areas

To develop the needed and ablest manpower in local areas

To develop the communication system globally

Strategies if IT policy 2002:

Carry on research, develop and expand information technology with a high priority. So as to increase participation of the private sector in IT development.

Prepare capable manpower with the involvement of both public and private sectors for sustainable development and expansion of information technology.

Encourage native and foreign investment for the development information technology infrastructure.

Legalize and promote e-commerce by using information technology.

Utilize information technology in the development of rural areas.

Include computer education in curriculum from the school level.

Increase export of services related to information technology.

IT policy: some of the policies to be followed for the implementation of the above mentioned strategies are as follows:

To declare information technology sectors as a prioritized sector.

To follow a single door system for the development of information technology.

To create a conductive environment that will attract investment in the private sector, keeping in view the private sector’s role in the development of information technology.

To provide internet facilities to all village development committees of the country.

To computerize the records of each government office and build websites for them.

To increase the use of computers in the private sector.

To develop physical and virtual information in technology park in various places with the private sector’s participation.

To use IT to promote e-commerce, e-banking, e-health, e-education, among others and to transfer technology in rural areas.

To establish National Information Technology Centre.

To establish a national level fund by mobilizing the resources obtained from Government of Nepal, donor agencies and private sectors so as to contribute to research and development of information technology and other activates associated with it.

To establish capital funds with the joint participation of public and private sectors.

To draft necessary laws that provides legal sanctions to the use of information technology.

To gradually use information technology in all types of government activities and provide legal sanctions to its uses in such activities.

Action Plan: These are some action plan to fulfill the objectives of IT policy.

Participation of private sector in infrastructure development.

Infrastructure development.

Human Resource Development.

Dissemination of information technology.

Promotion of E-Commerce.

Other related Facilities.

Legal provisions: Government of Nepal will design, update and implement the cyber laws from time to time as per national international situation. The law will be related to e-banking, digital signature, software piracy, data protection by encryption copyright protection and privacy protection act, etc.

Modification of IT policy: Government of Nepal will supervise the running of cyber law from time to time and rewrite them to update. In every two alternate years continuously, it will be updated.

NITCC: NITCC stands for National Information Technology Co-ordination Committee; its main purpose is to assist the development of IT in our country. Main functions of NITCC are as follows:

It provides the text books of National Communication System

It increases the status of people

It develops the man power and intentional works

NITC: NITC stands for National Information Technology centre. It is also governmental body to work for the development of IT in our country. It is established to develop the field of information system, to re-observe, to know yearly development and to solve the problems. It is form by twelve members including science and technology minister as president.

NITDC: It stands for National Information Technology Development Committee. It is form by eighteen members, where prime minister work as president and science and technology minister work as vice-president.

Cyber Laws, Ethics and Policies of Nepal.

Computer crime: Computer crime is a crime committed by the people through the use of computers.

Consumption of time of staff member in detecting intruders and managing safety methods.

Physical theft of computer and computer accessories which cause a huge damage of the assets.

Due to the attackers, the banks and financial companies get adverse publicity.

Vandalize the original web page with the different contents in WWW.

Lost of privacy due to the unauthorized access of information.

Safety from computer crime:

Protection of computer from power related problems by using power surges and power outrages.

Controlling and managing database and other very imp computer with authentication systems such as numbers.

Using call back systems to track the phone number which is used to connect.

Using firewall system to protect computer from external threats.

Using computer to protect from viruses.

Making backup regularly.

Computer related legal problems:

Plagiarism: The presentation of somebody’s work as if it were your own is known as plagiarism. For example some people or students copy the material from the internet and present them as if it is their own creation without prior permission from the authorized person to copy from the copyrighted material.

Software Piracy: Copying software CD or DVD is another big problem. People copy software and install in their computer. Some programs are freely available in the public domain under the provision of General Public License (GPL).

Digital signature: A security mechanism used on the internet that relies on tow keys, one public and one private, which are used to encrypt and to decrypt them on the receipt.

Public key infrastructure (PKI):PKI is a security management system including hardware, software, people, processes and policies, dedicated to the management of Digital Certificates (keys) for the purposes of secure exchange of electronic messages.

Private Key: One of the two keys in digital signature’s public key encryption. The user keeps the private key secret and uses it to encrypt digital signatures and to decrypt received messages.

Public key: One of the two keys in public key encryption. The user releases this key to the public, who can use it for encrypting messages to be sent the user and for decrypting the user’s digital signature.

Cyber law : The law which is practiced to control The following three basic types of computer crimes such as: theft of computer time for development of software, theft, destruction or manipulation of programs or data and alteration of data stored in the computer fileis called cyber law. Cyber law is the legal field that maintains the order of track in the internet access and communication.

The scopes that are covered by boundary of cyber law are as follows:

Intellectual property:

Computer crime law

Jurisdiction law

Digital signatures system

Privacy

Freedom of expression.

International cyber law:Now a day’s several cyber laws are applied to provide all types of computer security, software security and avoid computer crimes. Some famous and cyber laws are as follows.

Computer Matching and Privacy- right of government to keep the personal key record

protection Act 1988

Computer Ethics:Computer Ethics covers all the practical principles that deal with how the computer experts should make decisions in regard to the social and professional behavior. The term ‘computer ethics’ first devised by Mr. Walter Maner in mid 70s. But it is practiced from the beginning of 90s. The core issues of computer ethics incorporate:

Technological impact on the society.

Plagiarism

Intellectual property rights

Copyrights

Piracy

Hacking

Internet pornography and adult sites

Harassment and stalking etc.

Computer ethics for the computer user:

Respect yourself and do not give passwords to any second person.

Do not ask password and never try to know other’s password for any purpose.

Always give the credit to your originality.

Ten Commandments for computer ethics: The computer Ethics Institute of the Brookings Institute, Washington D.C has developed the following ethics:

Thou shalt no use a computer to harm other people.

Thou shalt not interfere with other people’s computer work.

Thou shalt not snoop around in other people’s files.

Thou shalt not use a computer to steal.

Thou shalt not to use a computer to bear false witness.

Thou shalt not to copy or use proprietary software for which you have not paid.

Thou shalt not use other people’s computer resources without authorization or proper permission.

Thou shalt no appropriate other people’s intellectual output.

Thou shalt think about the social consequences of the program you write or the system you design.

Thou shalt use a computer in ways that show consideration and respect for you fellow humans.

Computer Ethics for computer professionals:The codes of conduct and good practice for certified computer professionals are the essential elements of activity. They are:

A high standard of skill and knowledge.

A confidential relationship with people served.

Public reliance upon the standards of conduct in established practice.

The observance of an ethical code.

Ethical standards: A number of definitive sets of ethics have been developed to restrict the professionals in making harsh decisions and redirect them towards the right behavioral approach. Some of them include:

Association for Computing Machinery(ACM) codes of ethics is four point standards that govern the ethical behavior among the computer professionals.

Uniform Computer Information Transaction Act (UCITA) defines a set of standards related to the legal ethical behavior during the computer contract process.

Computer security:

In the 21 st century computer is most important part of our life. The computer itself is our great and very important property which holds several important data for the future use. So like other asset’s security computer security is very important.

The protection of computer system from accidental or intestinal harm, including destruction of computer hardware and software, physical loss of data, deception of computer users and the deliberate invasion of database by unauthorized individuals is called computer security. In short protection of computer, its accessories, data and programs for a long lasting of computer system is known as computer security.

Computer security is classified into two parts:

Hardware security

The protection of all hardware components used in computer system is known as hardware security. For the proper management of physical security of the computer, we have to maintain

Insurance is a very good method to protect other assets. Computer insurance helps us to insure our computer, if we lost it or parts are damaged or in case of calamities of theft loss of data.

Free of dust

Computer parts are very sensitive to dust. Dust can damage internal and external both parts of computer so to protect from dust we must put computer in very neat and dust free room. And we should use dust cover also to protect computer.

Protection from fire

Computers are easily damaged by fire. Electronic circuits of computers will get damage by fire or even smoke also. So we should not smoke near to computer and we should manage proper wiring because it may cause firing.

Protecting from theft

As computer is very valuable device like other assets, there is equal risk of theft for computer. We must keep it in very secure room. There must be lock in our computer and it is advised to keep grills in windows and safety lock in rooms.

Air condition system

Most of the electronic device gets damage in excessive heat. So room must be cool and dust free for computer. If there is excessive heat then computer parts may not work properly or it may stop functioning. It is suggested to maintain temperature between 18 o to 24 o Celsius and relative humidity of 50 to 60 percent. Micro computers can work up to maximum 30 oC also. But today’s new personal computers are designed to work even between 0 oC to 40 oC.

Power supply

Power supply is another cause of damage of computers. Computer needs 220V to 240V AC constantly. The voltage fluctuation may damage integrated circuits of computers chips because these are the most sensitive parts of computers. To protect from voltage fluctuation we must use UPS to protect our computers from sudden interruption of power because in such cases UPS provide power for some minutes to hours from backup battery inside it. Volt guard and Spike guards and Stabilizers are common device used in these days.

Furniture

Good and properly managed furniture is another factor to protect computer hardware. Tables and chair used in computer itself and to keep different storage devices of computers like floppy, pen drive, CD and DVD etc

Software security

The software is very important part of the computer. It includes programs and data or information store in computer. The protection of data and programs used in computer system is known as software security.Software security is required for the,

Prevention of loss of data,

Prevention of data and software program piracy

Prevention of corruption of data and

Prevention from error reading of data.

For protection of data and programs in our computer system, we should apply some security measures. Some common software security measures are as follows:

Password protection

Password is a set of characters that act like a key to unlock the system and other files and programs. Setting password in our files and user account to control the access of data and information in our computer is very good and effective method of software security. Password must be difficult to guess so we should not use common words as password. It is suggested to use the set of numbers, symbols and characters to create password.

Some common rules to create password:

Password length must be at least 6 characters.

The words used to set password must be difficult to guess

We should keep our password confidential

We must change password frequently

Files, which store password must be encrypted

Backup system

If data and information is very important. We must backup data regularly to other computer or other disk location and folders of the same computer so that we can restore it if data is corrupted or lost.

Data encryption and decryption

We can prevent the access of data or information by encrypting it. Windows operating system have built in feature to encrypt the data. If we encrypt the data computer will change the forms of this data and will not be readable or understood to other users. And if we have to give access we can decrypt it into original form.

Defragmentation

Defragmentation is the process of a file to contiguous sectors on a hard disk to increase the speed of access and retrieval. Because during long time files and folders store in computer will get fragmented or will be unmanageable in such case disk head will consume more time to read the data from the disk means computers becomes slower. So it is necessary to defragment the disk to increase the performance of the computer.

Firewall protection

Windows firewall is very important and useful tool to protect our computer from external and internal threat in LAN and Internet. While downloading files and programs form internet viruses and other person may try to access the resources of our computer. In such case windows firewall block such threats.

Scanning disk

Computer store all information in its disk surface. And hard disk is a main part where computer store all its information. So we must scan the surface of the to increase the performance of the computer. Windows provide some built in tools to scan the disk such as Scandisk and CHKDSK and several other utilities software are available to scan disk.

Hard lock key

Hard lock key is very important for software security. It is specially used to protect from software piracy. It is a kind of checking point available within the software during its running time.

DBMS and Microsoft Access

Introduction to Database System : In our daily life we encounter with various software. There is hardly any software that does not use database systems. The following are some of the widely used database systems:

Banking software

Airlines systems

University systems

Telecommunication systems

Finance

Sales

Manufacturing

Human resources

Data: Plural of the Latin datum, meaning an item if information. In practice, data is often used for the singular as well as the plural form of the noun. Data are information to the computer which are processed to get desired result and are the piece of information.

Information: The data which gives meaning or suitably arranged for communicating interpretation, and processed by human being by automated means such as computer is called information.

Database: A database is a collection of data that is organized so that its contents can easily be accessed, managed and updated.

File: A file is a collection of electronic information store in computer.

Record: A record is a information about an element such as a person, animal, students, place etc.

Filed: A filed is a piece of information about an animal, person, students, place etc. And these fields are the titles in the table of Ms-Access.

Data processing steps:

Data collection

Filtering

Coding

Data entry

List printing

List checking and editing

Updating

Final list printing

Final data preparation

Processing of final data

DBMS: A database management system (DBMS) is a computer program designed to manage a database (a large set of data), and run operations on the data requested by clients. For example Oracle, Microsoft Access, Ms. SQl, MySQl, dBASEIII+, dBaseIV, FoxPro, IMS, IDS, IDMS, ADABASE, CDS/ISIS, OMNIS, RBASE, SYSBASE, FOXBASE etc. are the well known database management system.

RDBMS: Relational Database Management System (RDBMS) is method of viewing information from several, separate database that relate to one another through the keyword or values. The main advantage of RDBMS is that we can simultaneously use more than one database to see information stored in them.

Importance of database:

Database stores the data.

Computerized database saves data from being lost.

Computerized database protects from unauthorized access and use of the data.

Data can be stored in a small area or space in computerized database.

Features of DBMS:

Easy to access data.

Ease to modify data.

Delete existing data.

Organize the data in proper sequence.

Sorting and indexing of data.

Easy queries in data.

Retrieve the data easily.

Print the formatted reports, labels etc.

Linking between two or more databases.

It can be used as SQl (Structured Query Language)

The Internet and E-mail:-

Internet: The internet is worldwide collection of computer networks and gateways that use TCP/IP suite of protocols to communicate with one another using telephone lines modems or satellites. Internet is network of networks. At the heart of the internet is a backbone of high speed data communication lines between major nodes or host computers, consisting of thousands of commercial governmental, educational and other computer system, that route data and messages.

Web site: Website is a location of the web pages created by any organizations, universities and government agencies to provide information regarding them like: http://www.bbc.co.uk/nepali,http://www.nepalnews.com etc. Each website has its own address that is also called internet address.

Web pages: Webpage is a collection of information that is stored in website. The www consists of huge collection of documents with related website called webpage. Webpage provides vast collection of information of related websites.

Browser: Browser is client software that allows the users to display and interact with the web page. For example: Internet Explorer, Netscape Navigator, Mozilla Firefox or Opera etc.

Web server: web server is a site on which the web pages are kept. It is a server computer that responds to requests from web browsers to relative resources.

Domain name: It is a name of specific internet area controlled by any organization, company or government.

Home page: The home page is the first hypertext document regarding the web address displayed when a user connects to any web server.

ISP( Internet Service Provider) A company that provides individuals or companies access to the internet and the world wide web is called ISP.

Firewall: software or hardware that limits the certain kinds of access to a computer from the internal network or external network.

E-Mail: E-mail stands for electronic mail. It is most widely used feature on the internet. Sending and receiving messages electronically through the internet is called E-mail. We can exchange any message with the people around the world by using e-mail. It is very easy and quick means of communication available in the computer world. We can write an e-mail message in an mail program like Eudora, Outlook Express, Netscape Navigator etc. and several web base program like Yahoomail, Hotmail, Gmail and Zapakmail are also used to send and receive e-mail.

E-mail address: Each E-mail address is identified by a unique name is called E-mail address. For example mailme@yahoo.com, ram@fewanet.com.np, etc. It has five parts they are as follows:

Ram : User’s name

@ (At the rate) : A separator symbol

Yahoo, fewanet : ISP address or domain name

.com or .edu or .net : commercial or educational groups

.np : Country code

Advantages of using E-mail:

It is cheapest and fastest means of communication and as compared our conventional postal mail.

It is more reliable than postal mail.

E-mail can be accessed from any part of the world and at any time.

Information can be share globally.

We can send photos, songs, video clips and other file with e-mail attachments.

A single mail can be send to multiple people at a time.

E-fax: E-fax stands for electronic fax. It is very powerful desktop application that allows us to send and receive faxes directly on our computer. It is very similar to e-mail. The E-fax first goes to the internet server then the internet server sends it to its destination whereas E-mail means first goes to the local file server.

Different between E-mail and E-fax:

E-mail

E-fax

1. It is very cheap.

1. It takes more cost than E-mail.

2. Message first goes to the local server.

2. Message first goes to the internet server and then to its destination.

3. Message is to be stored in the hard disk of the destination computer (server).

3. Message directly goes to print in the printer of the destination computer.

Computer language:

Programming:

The method used to develop a solution or a program is called programming. It is way of writing program using specific computer language to perform specific task.

Computer Language : The set of codes which is used to write computer program is called computer language . It is artificial language and can be used to define a sequence of instructions that can ultimately be processed and executed by the computer.

Types of computer language. :

Machine level language: The program written using machine code or binary numbers (0 and 1) is called machine level language. It is computer’s own binary-based language, or machine language, is difficult for human beings to use. It is machine dependent complicated and time consuming. It is also called first generation language.

Low level language (Assembly language) : The language which permits the use of mnemonics (which are combination of codes and English phrases) for each instruction that machine can do is called low level language. It remains in between machine level language and high level language. It is easier than machine level language and should be translated into machine code using assembler. It is also called second generation language. Example pseudo programming.

High level language : The language which uses plain English words or phrases and mathematical notation, following the correct syntax (Certain rules which are followed to write programs) is called high level language. It should be translated into machine code using compiler or interpreter. So they are slower. It is also called third generation language. Example: QBASIC, C, C++, LOGO, LISP, ADA, PASCAL etc.

Language processor : The set of program codes, which are used to translate program written in high level language or low level language into machine code, is called language processor. There are three types of language processor.

Interpreter : The language processor which converts High level language and Low level language into machine code is called interpreter. It translates programming codes line by line so it is slower than compilers and assemblers.

Compiler : The language processor which translates the program written in high level language into machine code is called compiler.

Assembler : The language processor which translates the program written in low level language into machine code is called assembler.

Source program : The original program written in high level language is called source program. It should be translated into machine code, so that computer understands and responses it.

Object Program : The program converted into machine code by compiler is called object program.

Advantages of high level language:

It is very simple because plain English words are used for programming.

There are pre-defined commands, which minimize the work of programmers.

All the commands are syntax driven, so they are very easy to learn and implement.

Features of high level language:

It is machine independent and problems oriented.

It does not require extensive mathematics knowledge and computer hardware knowledge.

It requires less time to learn and write the programs.

Provide better implementation and documentation.

Advantages of low level language:

I) The computation time of an assembly language program is less.

II) Program debugging is easier.

Disadvantages of low level language :

I) It is machine dependent.

II) Too difficult to learn and implement.

Bug and Debug : Any type of error in the program is called bug. The process of correcting bugs is called debug.

Introductions toC

What is C?

C is a programming language developed at AT & T’s (American Telegraph and Telephone) Bell Laboratories of USA in 1972. It was designed and written by a man named Dennis Ritchie. In the late seventies C began to replace the more familiar languages of that time like PL/I, ALGOL. It is general purpose high level programming language, which is used to develop business programs, text processing programs, database management programs and even to develop Operating System (OS).

Structured program:Structured Programming, in computer science, a general term referring to programming that produces programs with clean flow, clear design, and a degree of modularity or hierarchical structure. Benefits of structured programming include ease of maintenance and ease of readability by other programmers.

Advantages of C language: or Advantages of structured program:

A large and complex program can be divided into several simpler and manageable sub modules.

Support simultaneously coding of modules by multiple programmers at a time.

In today’s world of computer programming, there are many high-level languages to choose from, such as C, Pascal, BASIC, and Java. These are all excellent languages suited for most programming tasks. Even so, there are several reasons why many computer professionals feel that C is at the top of the list:

C is a powerful and flexible language. What you can accomplish with C is limited only by your imagination. The language itself places no constraints on you. C is used for projects as diverse as operating systems, word processors, graphics, spreadsheets, and even compilers for other languages.

C is a popular language preferred by professional programmers. As a result, a wide variety of C compilers and helpful accessories are available.

C is a portable language. Portable means that a C program written for one computer system (an IBM PC, for example) can be compiled and run on another system (a DEC VAX system, perhaps) with little or no modification. Portability is enhanced by the ANSI standard for C, the set of rules for C compilers.

C is a language of few words, containing only a handful of terms, called keywords, which serve as the base on which the language’s functionality is built. You might think that a language with more keywords (sometimes called reserved words) would be more powerful. This isn’t true. As you program with C, you will find that it can be programmed to do any task.

C is modular. C code can (and should) be written in routines called functions. These functions can be reused in other applications or programs. By passing pieces of information to the functions, you can create useful, reusable code.

Note: What is ANSI?

ANSI, in computer science, acronym for the American National Standards Institute, an organization of American industry and business groups dedicated to the development of trade and communication standards; internationally, the American representative to the International Organization for Standardization. In the microcomputer field, ANSI is commonly encountered in three areas: programming languages, the SCSI interface, and the ANSI.SYS device driver.

Variable : A entity whose value keeps on changing during the program execution is called variable.A variable is a name assigned to a data storage location. Program uses variables to store various kinds of data during program execution. In C, a variable must be defined before it can be used.

Rules for Constructing Variable Names

A variable name is any combination of 1 to 31 alphabets, digits or underscores. Some compilers allow variable names whose length could be up to 247 characters. Still, it would be safer to stick to the rule of 31 characters. Do not create unnecessarily long variable names as it adds to your typing effort.

The first character in the variable name must be an alphabet or underscore.

No commas or blanks are allowed within a variable name.

No special symbol other than an underscore (as in gross_sal) can be used in a variable name.

Ex.: si_int

m_hra

pop_e_89

These rules remain same for all the types of primary and secondary variables. Naturally, the question follows … how is C able to differentiate between these variables? This is a rather simple.

Keywords:Keywords are the words whose meaning has already been explained to the C compiler (or in a broad sense to the computer).

Keywords are also called as reserved word.

Constant:Aconstant is a fixed entity. It does not change its value during the entre execution.

Types of constant:

Integer constants

Floating point constants

Character constants

Enumeration constants

String literals.

Operator:An operator is a symbol that instructs C to perform some operation, or action, on one or more operands. An operand is something that an operator acts on. In C, all operands are expressions. C operators fall into several categories:

The assignment operator

Mathematical operators

Relational operators

Logical operators

The Assignment Operator: The assignment operator is the equal sign (=). Its use in programming is somewhat different from its use in regular math. If you write

= y;

in a C program, it doesn’t mean “x is equal to y.” Instead, it means “assign the value of y to x.” In a C assignment statement, the right side can be any expression, and the left side must be a variable name. Thus, the form is as follows:

variable = expression;

When executed, expression is evaluated, and the resulting value is assigned to variable.

Unary Mathematical Operators:Theunarymathematical operators are so named because they take a single operand where as binary takes two operands.(for example sum= 5 + 6 i.e here are two operands such as 5 and 6). C has two unary mathematical operators, listed in Table 4.1.

C’s unary mathematical operators.

Operator

Symbol

Action

Examples

Increment

++

Increments the operand by one

++x, x++

Decrement

–

Decrements the operand by one

–x, x–

The increment and decrement operators can be used only with variables, not with constants. The operation performed is to add one to or subtract one from the operand. In other words, the statements. This type of operator are extensively used with looping control statement such as for, while, do etc.

++x; means ++x; will increase the value of x and then processing takes place. –y; means –y; will decrease the value of y and then processing takes place. x++; means x++; will processes and then increases the value of x by 1. y–; means y–; will processes and then decrement will take place.

are the equivalent of these statements:

= x + 1; y = y – 1;

Binary Mathematical Operators: C’s binary operators take two operands. The binary operators, which include the common mathematical operations found on a calculator, are listed in Table 4.2.

C’s binary mathematical operators.

Operator

Symbol

Action

Example

Addition

+

Adds two operands

x + y

Subtraction

-

Subtracts the second operand from the first operand

x – y

Multiplication

*

Multiplies two operands

x * y

Division

/

Divides the first operand by the second operand

x / y

Modulus

%

Gives the remainder when the first operand is divided by the second operand

x % y

The first four operators listed in Table 4.2 should be familiar to you, and you should have little trouble using them. The fifth operator, modulus, might be new. Modulus returns the remainder when the first operand is divided by the second operand. For example, 11 modulus 4 equals 3 (that is, 4 goes into 11 two times with 3 left over). Here are some more examples:

100 modulus 9 equals 1 10 modulus 5 equals 0 40 modulus 6 equals 4

Relational Operators: C’s relational operators are used to compare expressions, asking questions such as, “Is x greater than 100?” or “Is y equal to 0?” An expression containing a relational operator evaluates to either true (1) or false (0). C’s six relational operators are listed in Table 4.4.

Table 4.5 shows some examples of how relational operators might be used. These examples use literal constants, but the same principles hold with variables.

C’s relational operators.

Operator

Symbol

Question Asked

Example

Equal

==

Is operand 1 equal to operand 2?

x == y

Greater than

>

Is operand 1 greater than operand 2?

x > y

Less than

<

Is operand 1 less than operand 2?

x < y

Greater than or equal to

>=

Is operand 1 greater than or equal to operand 2?

x >= y

Less than or equal to

<=

Is operand 1 less than or equal to operand 2?

x <= y

Not equal

!=

Is operand 1 not equal to operand 2?

x != y

Relational operators in use.

Expression

How It Reads

What ItEvaluates To

5 == 1

Is 5 equal to 1?

0 (false)

5 > 1

Is 5 greater than 1?

1 (true)

5 != 1

Is 5 not equal to 1?

1 (true)

(5 + 10) == (3 * 5)

Is (5 + 10) equal to (3 * 5)?

1 (true)

Logical Operators:Sometimes you might need to ask more than one relational question at once. For example, “If it’s 7:00 a.m. and a weekday and not my vacation, ring the alarm.” C’s logical operators let you combine two or more relational expressions into a single expression that evaluates to either true or false. Table given below lists C’s three logical operators.

C’s logical operators.

Operator

Symbol

Example

AND

&&

exp1 && exp2

OR

||

exp1 || exp2

NOT

!

!exp1

The way these logical operators work is explained in the table below

C’s logical operators in use.

Expression

What It Evaluates To

(exp1 && exp2)

True (1) only if both exp1 and exp2 are true; false (0) otherwise

(exp1 || exp2)

True (1) if either exp1 or exp2 is true; false (0) only if both are false

(!exp1)

False (0) if exp1 is true; true (1) if exp1 is false

Branching: Branching is based on decision making. If the decision satisfied, then it can perform the task, otherwise it executes the line next to it.

For example:

If ……….. else

If ……….. else if ………..else

Switch case

Looping: looping is a process which allows the data to be repeated unless or until some condition has been satisfied. The various statements are:

For

While

Do while

Comments : Comments are the statements that are used for user aid or remarks. The statements which are defined as comments are ignored by C compiler comments are non-executable statements. Comments are defined as /*…………your words…………..*/

Note : We defined comments as REMARK in QBASIC like REM ………. Or ‘…………

Escape sequence : The set of characters, which are not printed when used but provide various functions. Such escapes are start with ‘\’ back slash. For example

Character Escape Sequence

Bell (alert) \a

Backspace \b

Horizontal tab \t

New line \n

Carriage returns \r

Quotation mark \”

Backslash \\

Null

Identifiers: Identifiers are the name givne to various program elements such as variables, functions or arrays. It may consist both letter and digit but initial character must me letter and maximum 31 characters can be used to name the identifiers. For example: tax_rate, tax_year, year-2065 etc.

Library Functions: Various types of built functions which can be used to execute different types of task such as mathematical calculation, graphics management, memory management, data and file handling etc. Example: sqrt(), to lower (), to uppor () etc. #include directive: This is the most essential directive. A directive is links to a header files, the header file makes full use of the I/O functions of the C library. For example #include <stdio.h> Header files: The library function which is used to declare the source of file is called header file. For example: studio.h, conio.h, process.h, math.h, ctype.h, string.h, stdlib.h etc

} printf() : The printf a function used to send formatted output to the standard output device (monitor or printer) based on a format specification. scanf() :The scanf a function used to get formatted input to the standard input device (keyboard) based on a format specification. getch():The getch () function holds from screen scrolling. It is defined in stdio.h header files. void main():The void main() is appear in every C program. Main without void is used when there are no arguments. main() without any parameters has an argument.

Your First C Program

You’re probably eager to try your first program in C. To help you become familiar with your compiler, here’s a quick program for you to work through. You might not understand everything at this point, but you should get a feel for the process of writing, compiling, and running a real C program.

This demonstration uses a program named HELLO.C, which does nothing more than display the words Hello, World! on-screen. This program, a traditional introduction to C programming, is a good one for you to learn. The source code for HELLO.C is in Program01. When you type in this listing, you won’t include the line numbers or colons.

Program01 1.1. HELLO.C.

Be sure that you have installed your compiler as specified in the installation instructions provided with the software. Whether you are working with UNIX, DOS, or any other operating system, make sure you understand how to use the compiler and editor of your choice. Once your compiler and editor are ready, follow these steps to enter, compile, and execute HELLO.C.

Computer Virus

Definition: A computer program that can replicate itself by making copies itself without the user’s knowledge is called virus. Virus can destroys the data files, program files and system files of the computer.

Purposes of creating virus.

To protect software from software piracy.

To expose the programming capabilities of the programmer.

To sell anti-virus program and earn money.

To entertain the user by generating pictures and interesting messages on the screen.

For the criminal purposes such as to hack server computer of very sensitive organization or government offices.

Symptoms of computer virus. (What a virus can do to computer?)

Computer becomes slow by reducing memory space.

Computer may not boot and hang quickly.

System files may corrupt and affect the performance of computer.

Virus are self duplicating program hence it spread it occupy more space on the disk less space will remain for storing data or information.

Update the anti-virus program’s virus library to detect and eliminate new virus.

Never install pirated software.

Do not open e-mail attachment and e-mail from unknown person before scanning at first.

Write protect the disk when it need to use in another computer.

We must make backup copy of valuable data so it can be restored from original location in case of damage.

Practical Tips At Home: What to do if computer is already affected?

Solution:

Open computer in safe mode.(by pressing F8 key after you press power switch of CPU box)

Login computer by administrator or other account having administrative privileges.

Install antivirus program using program CD (CDs are good to install anti-virus program than Pen Drives because virus can transmit in pen drive before we install anti-virus and thus it can damage anti-virus program too) and scan the computer.

If cannot be install properly then we can restore the system in previous state (if Windows XP is installed in the computer) from System Tools option of Accessories option of Programs of Start button.

Again try from first step after you restore the system in previous state.

Types of computer virus:

There are many categories of viruses, including parasitic or file viruses, bootstrap-sector, program virus or file virus multipartite, macro, stealth virus and script viruses.

Bootstrap-sector virus:

Bootstrap-sector viruses reside on the first portion of the hard disk or floppy disk, known as the boot sector or Master Boot Record (MBR). These viruses replace either the programs that store information about the disk’s contents or the programs that start the computer. Typically, these viruses spread by means of the physical exchange of floppy disks. These viruses are also called as start-up infector virus. Examples of such viruses are Danish Boot, Devel 941, Disk killer etc.

Multipartite viruses:

Multipartite viruses combine the abilities of the parasitic and the bootstrap-sector viruses, and so are able to infect either files or boot sectors. These types of viruses can spread if a computer user boots from an infected diskette or accesses infected files. Examples of such viruses are Invader, Flip, Tequila, etc.

Parasitic or file viruses or program files:

Parasitic or file viruses infect executable files or programs in the computer. These files are often identified by the extension .exe , .bin, .sys, .drv etc. in the name of the computer file. File viruses leave the contents of the host program unchanged but attach to the host in such a way that the virus code is run first. Then it will affect execution of the program and hence the computer becomes very slow. Examples of such viruses are Acid Rain, Alien 298, Crazy, Brontok etc.

Script viruses:

Script viruses are written in script programming languages, such as VBScript (Visual Basic Script) and JavaScript. These script languages can be seen as a special kind of macro language and are even more powerful because most are closely related to the operating system environment. The ‘ILOVEYOU’ virus, which appeared in 2000 and infected an estimated 1 in 5 personal computers, is a famous example of a script virus.

Macro viruses:

Macro virus contains inside files. Macro command which is designed to infect a specific type of document files such as Ms Word or Ms. Excel files. Examples of such viruses are DMV, Nuclear and Word Concept.

Stealth viruses:

Stealth virus is one of the most dangerous types of viruses which really give information about the presence of it in the computer. Generally it infects the boot sector records and program files. It is difficult to detect using anti-virus program because it can hide in memory from the operating system and antivirus software. Some time they can hide other files. Examples of stealth virus are Frodo, Joshi, Whale, etc.

Microsoft Access

Microsoft Access is very powerful and most popular desktop database management system where we can create and maintain related data. It comes in a office package with other software such as Ms. Word, Excel, Power point etc. It is a relational database management system (RDBMS). In multi-user environment it supports file and data sharing mechanism. In access, we can store multiple databases and use them individually or in groups to create queries and reports or utilize two or more tables containing data arranged in rows and columns. Microsoft Access is a fully functional RDBMS. It provides all the data definition, data manipulation, and data control features you need to manage large volumes of data. It comes in different version such as, Microsoft Access 97/2000/XP/2003/2007.

Features of Microsoft Access:

It provides very useful database features such as tables, forms, reports and queries.

It works as front end development tool.

This provides end-user applications developer environment.

It shares data with other application such as Microsoft Word or Excel.

It support three computer programming language such as: SQL, Macros and Visual BASIC etc.

Notes:

End-user : The ultimate user of a computer, who has the need of use of computer database management system but lacks the time to learn all the complexities of the system or computer application in its finished, marketable form.

SQL: SQl stands for Structured Query Language. It is a tool that allows the database. It enables the users to extract, manipulate and related to learn data from one or more tables.

Macros:It is a list of actions which can be executed by clicking specific button is called macros.

Visual BASIC:It is very advanced and flexible and comprehensive language you can uses to dev lop complete user interactive applications.

Typical Uses for Microsoft Access

Here are just a few of the ways Access can fulfill the needs of a wide range of users.

Small Business

Accounting

Order entry

Customer tracking

Contact management

Consulting

Vertical market applications

Cross-industry applications

Sales and Marketing

Product promotion

Sales information resource

Order processing

Large Corporation

Workgroup applications

Information processing systems

Intranet publishing

Personal Use

Address book

Investment management

Cookbook

Collections—recordings, books, movies

Parts of Ms. Access

Table: A table is collection of data about a specific topic, such as products or suppliers. Using a separate table for each topic means that you store that data only once, which makes your database more efficient, and reduces data entry errors.

Table is the primary object of Ms Access. A table stores data in tabular form. A table is made up of rows and columns. Some parts of table are as follows:

Fields (column): The title name of the column that holds data is known as field. A table can have many fields.

Records (rows): The collection of data horizontally for each field is known as record. A record is complete information about an entity.

Data: The actual information stored under a filed title in a row is called data.

Index: A table can have index attached with it. The index is used to keep the data in organized for and helps faster retrieval of data.

Primary key: A primary key is a field which is uniquely identified. All the records of a table are uniquely identified on the basis of primary key. The column that has been defined as the primary key can’t hold null value. For example a student’s roll no. can be defined as primary i.e can’t be null and repeat.

Compound key: The primary key based on more than one field is known as composite key. It consists of multiple columns, because one column is not sufficiently unique.

Foreign key: Foreign key is the linking pin between two tables. It shows the relation between any two tables.

Queries: a query is search or question that you make for a record or item. The record is stored in the database file. Queries help to investigate about data records.

Forms: Forms present the data from a table or a query in a way we want it to be displayed. The fields in the table or query are made available to place on the forms we create.

Note: Use of form.

Displaying and editing data.

Controlling application flow.

Accepting input.

Displaying messages.

Printing information.

Reports: Reports are the printed results of data processing. Reports are specially formatted collections of data, organized according to your specification for summarizing and printing listings of database data. While forms are designed to be used onscreen, reports are designed to be viewed and printed.

Relationship: In a database we can establish relation between any two or more tables. Because no data are isolated, but they are associated or related with each other entity in one or another ways. we can generate reports and manipulate data using such relationship between tables.

Types of relationship:

Many to many relationship: A many to many relation is unclear. Many to many relations often are a sign that further analysis is required.

Many to one relationship: Many to one relation is the same as one to many, but from a different view point. Using this relation two or more fields of one table can be link with one field of another table.

One to many relationship: Most relation in tables are one to many, means one field of a table can be link with two or more fields of the another table.

One to one relationship: A one to one relation exception in database. It can be established using primary key and foreign key in the DBMS.

Note:Cascaded Delete: When deleting a row the RDBMS automatically deletes the related data in the many tables. This is called cascaded delete.

Keyboard Shortcuts for Scrolling in a Datasheet

Keys

Scrolling Action

Page Up

Up one page

Page Down

Down one page

Ctrl+Page Up

Left one page

Ctrl+Page Down

Right one page

Keyboard Shortcuts for Selecting Data in a Datasheet

Keys

Selecting Action

Tab

Next field

Shift+Tab

Previous field

Home

First field, current record

End

Last field, current record

Up arrow

Current field, previous record

Down arrow

Current field, next record

Ctrl+Up arrow

Current field, first record

Ctrl+Down arrow

Current field, last record

Ctrl+Home

First field, first record

Ctrl+End

Last field, last record

F5

Record number box

Ctrl+Spacebar

Select the current column

Shift+Spacebar

Select the current record

F2

Switch between selecting all data in the field and single character edit mode

Details of Data Type of MS. Access

Data type defines the nature of the data to be stored in the column. Access provided different types if data that can be stored.

Text: (Default) Test or combination of text and numbers, up to 255 characters.

Memo: Use for lengthy text and numbers, such as notes or descriptions. Stores up to 65,536 characters.

Number:Use for data to be included in mathematical calculations.

Date/Time:Use for dates and times Currency:Use for currency values and to prevent rounding off during calculations..

AutoNumber :Use for unique sequential (incrementing by 1) or random numbers that are automatically inserted when a record is added.

Yes/No :Use for data that can be only one of two possible values, such as Yes/No, True/False, On/Off. Nullvalues are not allowed.

OLE Object :Use for OLE objects (such as Microsoft Word documents, Microsoft Excel spreadsheets, pictures, sounds, or other binary data) that were created in other programs using the OLE protocol.

Hyperlink :Text or combination of text and numbers stored as a text and used as a hyperlink.

Lookup WizardUse to create a field that allows you to choose a value from another table or from a list of values using a combo box— -choosing this option in the data type list starts a wizard to define this for you.

Field Properties:

Field Property: Field size property is set to the maximum size for data stored in the field set to the text or number data type. For next data, the default field size is 50 and maximum size is depending on the type of data types.

Format: It allows choosing different format of data type available.

Decimal places: It is valid for only numeric data and currency data, where the decimal places numbers vary fro 0 to 15.

Caption: It used to display alternative name for the field to make the field name more explanatory. It can contain up to 2,048 characters.

Default Value: Default value is the one that enter automatically in the database and can be changed as per required.

Validation Rule: It is used to set the limitation while entering data in the database. It helps us to customize the data entry and checks for error entry of data.

Validation Text: If wrong data is entered which do not supported by given validation rule, it is used to display messages on the screen and work as a precaution of wrong data entry.

Required: If required is set as Yes then field should always receive a value during data entry.

Indexed: You can choose whether you want to index the table. The available index options are unique index and duplicate index.

Input Mask: It is usually used to set control the data entry in the database. Using this option we can customize the data entry by setting special commands using the following symbols:

Decimal placeholder and thousands, date, and time separators. (The actual character used depends on the regional settings specified in Microsoft Windows Control Panel.)

<

Causes all characters that follow to be converted to lowercase.

>

Causes all characters that follow to be converted to uppercase.

!

Causes theinput mask to display from right to left, rather than from left to right. Characters typed into the mask always fill it from left to right. You can include the exclamation point anywhere in the input mask.

\

Causes the character that follows to be displayed as a literal character. Used to display any of the characters listed in this table as literal characters (for example, \A is displayed as just A).

Password

Setting the InputMask property to the word Password creates a password entry text box. Any character typed in the text box is stored as the character but is displayed as an asterisk (*).